Foot controlled continuously variable preference circuit for musical instruments



Sept. 22, 1970 B. J. PLUNKETT ETAL FOOT CONTROLLED Filed Feb. 24, 1967CONTINUOUSLY VARIABLE PREFEREN CIRCUIT FOR MUSICAL INSTRUMENTS 2Sheets-Sheet l AMPLIFIER INSTRUMENT FIG.

INVENTORS BRADLEY d. PLUNKETT LESTER I KUSHNER I r ATTY FREQUENCYhank-JO FIG. 3

p 1970 B. J. PLUNKETT ETAL 3,530,224 FOOT CONTROLLED commuousw VARIABLEPREFERENCE CIRCUIT FOR MUSICAL INSTRUMENTS 2 Sheets-Sheet 2 Filed Feb24, 1967 FIG. 5

JNVENTOR.

BRADLEY J. Pumnnr BY LESTER L. Kusuum ATTY United States Patent O f FOOTCONTROLLED CONTINUOUSLY VARIABLE PREFERENCE CIRCUIT FOR MUSICAL INSTRU-MENTS Bradley J. Plunkett, Van Nuys, and Lester L. Kushner,

North Hollywood, Calif., assignors to Warwick Electronics Inc., Chicago,TIL, a corporation of Delaware Filed Feb. 24, 1967, Ser. No. 618,359Int. Cl. Gltlh 1/02 U.S. Cl. 84-1.11 7 Claims ABSTRACT OF THE DISCLOSUREIn a musical instrument a resonant circuit is connected in the circuitbetween the tone generators and the loudspeaker. The tone generatorsdeliver tone signals rich in harmonics covering a wide frequencyspectrum. Within this spectrum a given frequency (or a narrow band offrequencies) is given preference in the delivery path of the tones fromthe tone generators to the loudspeaker. The position on the frequencyscale of this preferred requency or resonant peak is continuouslyvariable, from low frequency to high frequency over the wide frequencyspectrum. This variability is under the ready control of the instrumentplayer, as for example by being connected to a foot pedal. Thus, duringplaying of the instrument, the player can continuously move the resonantpeak back and forth across the frequency spectrum and create a rhythmicmusical sound. The musical effect may be described as a wow-wow and isclosely akin to that produced by the warbling of a trumpet mute acrossthe bell of a trumpet.

BACKGROUND OF THE INVENTION Electronic musical instruments are becomingmore and more popular among musical groups. In some cases, for example,in an electronic organ, the tone itself is generated electronically andtreated in its electric signal state in numerous ways, finally emerging,for the first time as a vibration or acoustic signal, from theloudspeaker of the system. In other musical instruments the tone isgenerated mechanically, as for example by vibrating a guitar string orblowing into a wind instrument. The mechanical or acoustic vibration isthen picked up and translated into an electric signal. The electricsignal is then acted upon in a variety of ways by numerous electroniccircuits, and then emerges once more to acoustic form in the loudspeakerof the system.

In years past, for example in dance bands, certain trumpet players haveproduced a unique effect which may be described as a WOW-WOW. This isdone by holding a mute over the bell of the trumpet and moving the muteso as to in effect rhythmically open and close the bell passage. Whendone skillfully the effect can almost simulate the human voice. Arudimentary practice of the effect, as noted hereinbefore, produces asound closely akin to a persons singing wow-wow-wow. Heretofore, thiseffect has been largely confined to horns, such as trumpets, and hasrequired skillful manipulation of a mute over the bell of the horn bysophisticated horn players.

SUMMARY The present invention consists of an electronic circuit ICC bymeans of which the artist or player of any electronic musical instrumenthas at his control a lever, such as a foot pedal, through which he canclosely simulate the wow-wow sound previously limited to the trumpet, asnoted hereinbefore. The invention may be applied to any musicalinstrument in which electric tone signals are produced, whether suchsignals are initially produced electronically or whether they areproduced acoustically, and then translated into electric tone signals bymeans of pickup devices. It is particularly adaptable to hand-heldinstruments, such as wind instruments, guitars and other stringinstruments and the like. The present invention consists of a resonantcircuit which favors or discriminates in favor of a particularfrequency, or narrow band of frequencies, in the translation pathbetween the tone generators and the loudspeaker. -By continuously movingthis favored frequency back and forth across the frequency spectrumrhythmically, as with a foot pedal, the player can simulate the wow-wowsounds previously done acoustically by sophisticated trumpet players.

In a preferred form of the invention the frequency tuning isaccomplished by means of an amplifier circuit having negative feedbackand so connected that the apparent input reactance of the totalamplifier circuit may be varied in accordance with the gain of theamplifier. This reactance, for example a capacitive reactance, iscoupled with a complementary reactance, e.g., an inductor, to form avariable frequency resonant circuit, the frequency position of whichdepends on the gain of the amplifier at that particular moment. Theamplifier is so designed that the gain may be controlled by acontrollable member, such as a potentiometer, which is readily placedunder the manual or pedal control of the instrument player or performer.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, FIG. 1 is a blockdiagram of the musical circuit. FIG. 2 is a circuit diagram illustratingthe variable frequency circuit of the present invention. FIG. 3 is agraph illustrating the effect of the variable frequency circuit on theoutput of the musical system. FIG. 4 is a side view of a pedal designedto inject the wow-wow effect into the circuit. FIG. 5 is an end view ofthe pedal.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 there isshown an amplifier 13 having an input 11 and an output 12. To the input11 there is designed to be applied an electric tone signal andespecially an electric tone signal rich in harmonics. This signal may begenerated electronically, e.g., in an electronic organ, or may begenerated acoustically, e.g., by vibrating the strings of a guitar 9, orin the mouthpiece of a wind instrument, and then translated into anelectric signal by any form of known pick-up device.

The output 12 is adapted to be connected ultimately to some form ofspeaker means or electro-acoustic trans ducer 10. Interposed between theoutput 12 and speaker may if desired be any form of amplifier, formantcircuit, tone control circuit, or other musical instrument circuitry,exemplified generally at 15.

Referring to FIG. 2 the amplifier =13 interposed between the input '11and the output 12 consists of two stages, the first stage including thetransistor 14, and the second stage, the transistor 16.

The input 11 consists of a jack having a B terminal 17, a groundterminal 18, and a hot or signal terminal 19. When the plug from thetone signal generator 9 is plugged into the jack 11, signal voltage isapplied between the terminals 17 and v19, and simultaneously theterminal 17 is connected with terminal 18. The plug thus serves thedouble function of injecting signal into the system and also energizingthe circuit by connecting the negative side of the energizing battery 21to ground 18.

Tone signals are applied from the input terminal 19, through a couplingcapacitor 22 and resistor 23, to the base 24 of the transistor 14.Amplified output is taken from the collector 26 through the couplingcapacitor 27 and applied to a variable resistance means in the form of apotentiometer 28. The slider 29 of the potentiometer 28 is connectedthrough a coupling capacitor 31 to the base 32 of the second stagetransistor 16. The transistor 16 is connected as a low output-impedanceamplifier of approximately unity gain, i.e., as an emitter follower.

Output from the second stage 16 is taken from the emitter 33 through afeedback impedance, in the form of a feedback capacitor 34, to the inputto the amplifier, i.e., to the base 24, through a resistor 36.

The first stage 14 amplifies and inverts the applied tone signal.Because of the amplification of the signal applied across the feedbackcapacitor 34, the apparent reactance, seen by the input signal lookinginto the capacitor 34, is much lower than the actual reactance. Theinput impedance into the transistor 14 on the other hand is relativelyhigh. Thus, so far as current flow is concerned, as a practical matter,the signal looks primarily into the reactance 34, the apparent magnitudeof which, as noted, depends on the gain of the signal in passing throughthe amplifier. This gain is determined by the position of the slider 29of the potentiometer 28. When the slider is farthest to the right inFIG. 2, the gain is minimum; the current fiow through the feedbackcapacitor 34 is minimum; and, hence, the apparent reactance is maximum,i.e., the apparent capacitance approaches the true capacitance, viz, arelatively small value. When the slider 29 is in its left-hand positionin FIG. 1, the gain is maximum; the current through the capacitor 34 ismaximum; the apparent reactance 34 is minimum; and, hence, the apparentcapacitance of 34 is a maximum.

There is thus presented to the input signal appearing at the junctionpoint 37, a relatively pure capacitive reactance, the magnitude of whichis dependent upon the gain in the amplifier, i.e., upon the position ofthe slider 29. There then remains only the matter of connecting acomplementary reactance, in this case an inductor 38, in circuit withthe capacitor 34, to produce a resonant circuit, the tuning of which maybe adjusted by tuning the apparent magnitude of the capacitor 34.

The output from the amplifier is taken from the junction point 39,between the capacitor 27 and potentiometer 28, and applied through adouble-throw switch 41 to the output jack 12.

The operating characteristics of FIG. 2 will be readily understood byreference to FIG. 3, wherein the ordinate represents output signalappearing at the output jack 12 and the abscissa represents frequency ofthe tone components in the harmonic-rich tone applied to the input 11.When the slider 29 is moved to the left the net gain in the amplifier ishigh and the apparent capacitance of 34 is likewise high, so that theresonance frequency of the LC circuit 34/38 is relatively low. Hence thecircuit in this condition gives decided preference to the low frequency,exemplified at peak 41 in FIG. 3. Conversely when the slider 29 is movedto the right, the amplifier gain is low, the apparent capacitance of 34is likewise low, and the circuit peaks at 42. The peak can be positionedanywhere in between simply by positioning the slider 29 between itsextreme positions.

The aggregate Q of the circuit is quite high, thereby giving decidedpreference to the selected frequency (or narrow frequency band). This isseen in FIG. 3, where the peak output at 41 is many times, eg 10 times,the output at the other frequencies, represented by the relatively fiatline at 43. The innate Q of the circuit, in fact, is so high that it wasfound desirable to insert the resistor 36 in order to admit some of thenon-favored (offpeak) frequencies into the amplifier, so that they couldpass to the output. Without the resistor 36, virtually the onlyfrequency appearing at the base 24 would be the selected frequency,because of the high Q of the circuit. The presence of resistor 36 allowsall frequencies to be developed to a certain extent thereacross, andhence to be passed to the amplifier.

The function of the other components in FIG. 2 will now be described.Resistor 44 constitutes the DC load for the collector 26 of thetransistor 14. Resistors 46 and 47 form a voltage divider fordetermining the bias applied to the base 24 through the inductor 38 andresistor 36.

The bias for the second stage, transistor 16, is obtained from thecollector 26 of the first stage 14, through the resistor 48. The emitterfollower 16 has some slight tendency to oscillate. The inclusion ofresistor 49 in its collector circuit supresses any parasiticoscillations,

Resistor 52 is a DC return resistor for the emitter follower 16.Resistor 53 is a DC return for the emitter of transistor 14. Capacitor54 constitutes an AC return path for the tuned circuit 38/34, and alsoserves as a bypass for AC around the bias network resistor 47.

It will be noted that the output, being taken from the point 39, isunaffected by the position of the potentiometer slider 29. Therefore theposition of the slider 29 does not change the overall amplification ofthe circuit, at the output 12. Its only effect is to move the resonantfrequency peak back and forth along the frequency scale, shown in FIG.3.

When the wow-wow etfect is not desired, the double throw switch 41 isthrown to the upper position, which bypasses the amplifier and sends thesignal directly from the input terminal 19 to the output jack 12. Itwill be noted that even in this position of switch 41, the input to theamplifier is still attached to the circuit, through the permanentlyattached coupling capacitor 22. This produces a slight hump at thefrequency to which the amplifier is set, but the effect is so slight asnot to be audible to the ear. That is, at the peak frequency theamplifier presents to the bypass conductor 51 an impedance which isapproximately the sum of resistor 23 (68 kilohms) plus the parallelimpedance of the resonant circuit 38/34, which is about 15 kilohms. Thistotals approximately 83 kilohms. At off peak frequencies, the impedanceis essentially the 68 kilohms of resistance 23, plus the resistance ofresistor 36, about 1.5 kilohms. This difference in loading placed on thebypass circuit 51, as noted, does produce a slight hump at the resonantfrequency, but it is not enough to be discernible by the ear.

As noted hereinbefore, the slider 29 is attached to some form of leveror operating member which is readily controllable by the instrumentplayer. In the case where the tone generator which produces and deliversthe basic musical tone to the input 11, is an instrument such as aguitar 9 held by both hands of the player, this operating lever mayconveniently take the form of a foot pedal, which is rocked back andforth to produce the wow-wow sound discussed hereinbefore.Alternatively, the lever may be a rocker arm attached to the face of theguitar, for example, a bridge member which may span the guitar stringsand be rocked back and forth, somewhat in the way that a mute control ismoved to apply a muting pad to the strings of the guitar.

In place of the potentiometer 28 having the movable slider 29, there maybe light dependent resistor (LDR) which constitutes one segment of avoltage divider. The output to the second stage 16 is taken from thejunction point between a fixed resistor and the LDR. In this case thevoltage division is continually dependent upon the magnitude of the LDR,and, hence, upon the amount of light falling on it. By giving theinstrument player or performer control over the amount of light fallingon the LDR, he can be given control of the gain of the amplifier and,hence, control of the position of the frequency peak 41 (FIG. 3).

A satisfactory circuit has been constructed as shown in FIG. 2 havingthe following parameters.

Transistor 14-2N3900A Transistor 16-2N2924 Resistor 23-68 kilohmsResistor 36-15 kilohms Resistor 47-100 kilohms Resistor 46-470 kilohmsResistor 53-470 ohms Resistor 44-22 kilohms Resistor 48-470 kilohmsPotentiometer 28-100 kilohms Resistor 49-1 kilohm Resistor 52-10 kilohmsCapacitor 22-001 microfarad Capacitor 54-4 microfarads Capacitor 27-022microfarad Capacitor 340.01 microfarad Capacitor 310.22 microfaradInductor 38-500 millihenrys Battery 21-9 volts Another feature of theinvention is the construction of the foot pedal which operates theslider 29 of the potentiometer 28. This foot pedal is so constructed asto conveniently gang the slider 29 and the double-pole switch 41, insuch a manner that the instrument player may conveniently operate boththe slider 29 and the doublethrow switch 41 by appropriate manipulationof a single pedal.

This configuration is shown in FIG. 4, wherein 61 represents a base towhich a foot pedal 62 is hinged at 63. The pedal 62 is so mounted thatby downward movement of the toe the pedal may be rocked down toward thebase 61, while by pressing back with the heel against the rear of thepedal 62, the toe end of the pedal may be raised from the base 61. Bymeans of a rack 64 and pinion 65, the rocking of the pedal 62 is coupledto a shaft, shown figuratively at 29 in FIG. 4, which in turn actuatesthe slider 29 back and forth across the potentiometer resistance 28.

The double-throw switch 41 is mounted on top of the base 61, just underthe toe of the pedal 62. Switch 41 is a conventional type of switch,characterized by an operating member or element, in this case areciprocable plunger 66, which is biased upwardly and which returns toits starting or upward position after each actuation. The plunger 66thus always moves through a given cycle of movement, up and down, witheach actuation. Each cycle of movement, i.e., pushing down and releasingon the plunger 66, causes the double-throw switch 41 to move from eitherposition to the other. Thus, assuming the arm 72 of switch 41 is in thelower or wow-wow position (FIG. 2) and the underside of the pedal 62 isbrought against the plunger 66 and pressed down, the arm 72 will bethrown to the upper or by-pass position. The pedal 62 is then returnedto a normal position, out of contact with the switch plunger 66. Thenext identical operation of the foot switch 62 on the plunger 66 willcause the plunger to go through exactly the same reciprocating cycle,but this time the arm 72 of switch 41 will be thrown back to the loweror wow-wow position.

The lower (counterclockwise, FIG. 4) position of the pedal 62 is, ofcourse, at one extreme of the slider 29 in its passage across theresistor 28. For example, this may be the right-hand end of resistor 28in FIG. 2, i.e., where the circuit represented by 38/34 is tuned to itshighest frequency.

Thus, to switch the wow-wow circuit in or out, the instrument playerneed only move the pedal 62 to its extreme downward position. Theterminal operation serves to actuate the plunger 66 and thus switch thedoublethrow switch 41 to its other position. In this way the wowwowcircuit may be conveniently placed in or out of the instrument circuitwithout requiring any special operation by the player, since his foot isalready on the pedal 62 ready to operate the wow-wow effect(potentiometer 28/ 29) whenever the arm 72 of switch 41 is in its downposition (FIG. 2).

In practice it is preferred to construct the potentiometer 28 so that atthe switch operating end, there is no variation in resistance. Thus,during that portion of the movement of pedal 62, where the switch 41 isbeing operated, no change in the resonant frequency of the circuitoccurs.

In order that the switch 41 be not accidentally operated there areprovided a pair of rubber bumpers 67 projecting downward from theunderside of the pedal 62 on each side of the switch 41. These bumpersengage the base 61 about the time the pedal 62 comes into contact withthe switch operating plunger 66. Thus, the instrument player mustincrease the force on the pedal 62 greatly in order to overcome theresistance of the bumpers 67, thereby com pressing them and forcing thepedal down against the plunger 66 far enough to actuate the switch 41.Upon release of this extra pressure, the rubber bumpers aid in returningthe pedal 62 to a position clear of the actuating plunger 66.

The slider 29 and switch 41 are thus to a certain extent ganged togetherby the foot pedal 62. This ganging is represented schematically by thedotted line 71 in FIG. 2. While the present invention has been shown anddescribed herein in what is conceived to be the most practical andpreferred embodiment, it is recognized that departures may be madetherefrom within the scope of the invention which is, therefore, not tobe limited to the details disclosed herein, but is to be afforded thefull scope of the claims.

What is claimed is: 1. A circuit means adapted to be inserted between amusical instrument and a speaker means, said instrument including tonegenerating means for delivering electric tone signals corresponding tomusical sounds, and said speaker means serving to transduce said tonesignals into musical tones; said circuit means being adapted to haveapplied thereto from said instrument, electric tone signals in apredetermined frequency range lying within the range of said electrictone signals delivered by said tone generating means for passing saidelectric tone signals delivered by said tone generating means forpassing said electric tone signals from said tone generating means tosaid speaker, and said circuit means including:

network means for favoring the delivery of certain signal frequencies ina narrow frequency band within said predetermined frequency range fromsaid tone generating means to said speaker means, and

foot-operated control means physically separated from said instrumentand readily controllable by the foot of the instrument player forcontinuously varying said narrow frequency hand back and forth over saidpredetermined frequency range.

2. The combination defined in claim 1, in which said network meanscomprises a resonant network having a high Q relative to said circuitmeans to exhibit a sharp peak amplitude/frequency responsecharacteristic superimposed on the aforesaid substantially uniformresponse characteristic, and extending to an amplitude representing asubstantial multiple of the corresponding amplitude of said uniformresponse characteristic, the position of said narrow frequency band insaid frequency range being established by the resonant frequency of saidresonant network, and said foot-operated control means serving to varysaid resonant frequency so as to move said narrow frequency band backand forth over said predetermined frequency range.

3. The circuit means defined in claim 2, wherein said footoperatedcontrol means comprises a potentiometer, the position of whichdetermines the apparent magnitude 7 of a resonant frequency-determiningreactance element forming a portion of said resonant network.

4. The circuit means defined in claim 2, wherein said resonant networkcomprises: a variable gain amplifier having feedback means for creatingan apparent resonant frequency-determining reactive input impedance tosaid amplifier, the magnitude of which depends upon the gain of theamplifier, and wherein said foot-operated control means comprises meansfor varying the gain of said amplifier.

5. The circuit means defined in claim 4, in which said amplifiercomprises: a first stage of amplification, variable resistance means inthe output of said first stage, a second stage of amplification havingits input taken from said variable resistance means, a feedbackimpedance connected from the output of said second stage to the input ofsaid first stage, whereby variation of said variable resistance meansvaries the resonant frequency-determining apparent reactive inputimpedance of the amplifier.

6. The circuit means defined in claim 5, in which said variableresistance means comprises a potentiometer.

8 7. The circuit means defined in claim 5, in which said second stage ofamplification is a low impedance amplifier of approximately unity gain.

References Cited OTHER REFERENCES Kerchner-Corcoran: Alternating-CurrentCircuits, 3d ed. 1958, pp. 121-123.

WARREN E. RAY, Primary Examiner U.S. Cl. X.R.

